Why can't I ollie down staires?

I've been skating for about 3 years on an off and about 2 years ago i could ollie down a 5 set no problem, i then stoped skating for abit and never really went back to ollie staires and now i try to ollie down 'em again and i just can't not even a small 3 set i just bail out everytime and i don't know why its not like i even feel scared :/ why can't i do it anymore!?